Incorrectly tightening bolts and screws on your bike, can become very expensive.
As bicycle component manufacturers strive to improve the performance of their products, the tolerances to which these parts are manufactured become more exact.
The need to assemble these components with a torque wrench has therefore become imperative. Carbon-fibre is most susceptible to damage from over-tightening, but the fasteners on all bicycle components should be treated with care when tightening.
As a threaded fastener is tightened, the fastener flexes and stretches. This stretching is not permanent but gives the joint force to hold the components together. Each fastener is thus designed for a certain range of tension and over-tightening will deform threads or parts.
By the same logic, fasteners that are not torqued enough, will loosen and this too can cause damage to components. Riding with a loose bottom bracket could cause damage to your frame for example.
Tightness or torque is measured in Newton Metres (Nm). A torque wrench is your tool for setting fastener tension. Tightening of fasteners to manufacturer specifications prevents component damage or components coming loose, which can trigger a crash when riding.
Manufacturers could choose not to honour a warranty claim if components were damaged due to them not being torqued correctly.
Most components, including your stem, seat post clamp and bottom bracket (BB) will have the recommended torque settings etched alongside the fastener.
If the components are not marked, the owner’s manual for that particular component, most of which are available online, will list the recommended torque settings.
A good workflow idea is to keep a list of the various torque figures applicable to your bicycle alongside your workspace.
The majority of fasteners on a bicycle need to be tightened to figures below 10Nm, but items like your bottom bracket need to be torqued to approximately 50Nm.